Overheated 351W. What to check?

The raw water intake hose on my 1983 Ski Nautique (351W engine) came disconnected and I overheated the engine pretty badly. I didn't notice until the temp gauge was pegged and there was a burning smell. I also saw some white smoke coming from the doghouse and exhaust initially.

After letting it cool down and inspecting the impeller (which somehow was fine), the engine revs fine out of gear but in gear it's really rough and dies around 3000RPM, I was able to idle back to the boat ramp. There doesn't appear to be any water in the oil and the crankcase level hasn't changed at all from before I left for the day.

At home I hooked it up to some water and it seems to run ok without any smoke but it is harder to start than it was before. I also noticed some water spraying inside the boat and discovered it apparently got hot enough to partially deform one of the plastic mufflers. I did a compression test after warming the engine and got the following (in 1-8 cylinder order): 130, 130, 120, 130, 135, 135, 130, 140. Still no evidence of water in the oil.

I'm kind of stumped on where to go from here. Are those numbers bad? 3 looks low and 8 looks high but I don't know if they're far enough apart to worry about. What else do I need to do to pinpoint the issue? Is there possibly a transmission issue? Any help would be appreciated.

I've inspected the exhaust hoses. The port side looks fine. The starboard looks fine after the muffler but everything from the muffler to the riser is toast. New parts are on the way for that. Would a melted hose be enough for it to bog like it did under load? Exhaust and water were coming out. They just happened to be coming out in the boat.

A friend of mine is helping me do a leakdown either tonight or towmorrow. If that looks good I plan to do a water test to see if it runs properly. Is there anything else I should do before putting it back in the water?

hal2814 wrote: I've inspected the exhaust hoses. The port side looks fine. The starboard looks fine after the muffler but everything from the muffler to the riser is toast. New parts are on the way for that. Would a melted hose be enough for it to bog like it did under load?

SNobsessed wrote: Sounds like one or both of your exhaust hoses melted internally. .

As Chris mentioned, the damage would be internal. The typical failure from an overheat is the inner ply of rubber delaminates and collapses.

The Rubber exhaust hose that connects to your exhaust manifold is designed to help shut down your engine if you run dry with no water in the exhaust. The inner tube is supposed to collapse and shut off your exhaust making the engine choke itself and give you a warning that something is very wrong prior to you burning a hole through the exhaust tube.
Normally if one goes dry they both go dry and you will need to replace both.
They are expensive but serve a purpose so stay with Marine exhaust hose for replacement. If one of yours is still good and the inner tube is intact it must have had some cooling on that side while the other melted.

Hollywood is dead on, the melted hose chokes your exhaust and shuts down your engine by cutting off exhaust flow. I have not seen one kill the engine completely but both times I witnessed the hose collapse the engine started running terrible about the time we figured out we had lost water flow and burned up the exhaust tubes.
In the two cases I was present for both engines had zero overheat damage, the tubes shut us down before damage was done to the engine. The Marine hose is expensive but a new engine would have cost far more so they are worth every penny in addition to being required by law and safer.

A little dish soap works really well to ease the installation process and dish soap will not cause any rubber rot to haunt you later.   Glad you got it back together, keep us posted on your results.

hal2814 wrote: Now the starter is occasionally clicking when hot instead of turning over. It probably got wet. I took on quite a bit of water. I guess I;ll be replacing that next. Still cheaper than an engine.

Eric,
No on the new starter until you do some testing. Check you battery cables and their terminals. What condition is the battery in? Get it tested if unknown. Use a starting battery and not a deep cycle. Don't just start throwing parts are a problem. As far as the starter getting wet, think about how wet an automotive gets every time you drive in the rain and through puddles!!!

SNobsessed wrote: Starter might just need brushes. An auto electrical shop can do that for less than a new starter.

Or, if after testing that the starter is getting the volts, open it up yourself, clean up the commutator and install a new set of brushes

hal2814 wrote: But my experience on the automotive side tells me that if it's only having problems when the engine is warmed up (especially on 100f+ days) it's probably the starter. I may look into doing the brushes if I can confirm it is the starter.

Advanced timing can cause the above trouble too. When was it checked last?

Timing shouldn't impede the starter turning over.    I too had hard hot starting at 10 BTDC, but it turned over OK, just acted flooded.

Eric,
Keep checking the volts before jumping at the starter. On the start relay (solenoid), get an Ohm reading across the contacts to see if they are burnt. Regarding that new battery, hopefully you got a starting and not a deep cycle.

Yes, a starting battery is what I bought. I forget the exact specs but it's in line with what's recommended in the PCM manual and not too far off from the 5 year old battery that was in the boat before.

I set the timing back to 6 and it didn't matter. It worked fine all morning but when the engine (and afternoon) got hot the starter acted up again. I don't think it's turning the flywheel. It sounds like the starter is spinning but not engaging. Voltage looks good to the starter. Resistance on the relay looks good. It's only intermittent right now. It acts up once or twice then cranks fine. I found a reasonably priced starter and am going to go with that.

I did also notice an drip from one of the exhaust manifold gaskets so I'll be replacing both of those Fortunately, I'm not seeing water in the oil so I assume it's just an external leak. I'm also doing the riser gaskets while I'm at it. I'm not 100% sure that's a result of the overheat but I'll chalk it up to that. Do I need to RTV the gaskets or prep them in any way other than cleaning the mating surfaces?

The only other thing to be aware of is the orientation of the riser gasket. It's designed to block the passage towards the exhaust outlet.

Refer to skidim's page:
http://www.skidim.com/50L_58L-302_351-FORD/products/1158/

Thanks for the tip on the riser gasket. I've seen that it's not symmetrical and has that tab. I'll make sure to install it in the proper direction.

I have the starter now and plan to replace it today. I don't remember the exact numbers on voltage and resistance. I'm friends with a professional mechanic who helped me do those tests. I trust his judgement on that.

Gaskets should be in tomorrow. Does anyone know the size of the hex bit I need for the exhaust manifolds?

I never gave an update and I hate it when people do that so here it is:

The new starter works fine.

There was an external water leak coming from the riser and leaking onto the exhaust manifold. I replaced the riser and exhaust manifold gakets but due to the water leak those two bolts where the water was leaking were a bear to take off. I took the boat to a car mechanic to get those them off. With the manifolds off I also noticed a small oil leak coming from the valve cover gasket so I replaced that, too.

I put everything back together and the engine ran rough. I think the shop torched those bolts to get the manifold off and left the spark plugs on because one of the plugs was failing intermittently. I replaced the offending plug and the boat runs like a champ now. Thanks everyone for the help!

I did just notice a small transmission fluid leak but I'm not sure if that could be caused by an overheat. I'll look further into that. I'm not even sure where it's coming from yet. I just noticed maybe a teaspoon of tranny fluid in the bilge when I prepped the boat to go out last. Fluid level was still fine. Unless someone thinks that could be related to an overheat I'll start a new thread on it when I have more info.